The subject matter disclosed herein relates to visual inspection systems, and more specifically to ways of evaluating the performance of such systems.
Remote visual inspection (RVI) systems, e.g., borescopes, permit viewing features that are not directly accessible by human inspectors, such as turbine blades. RVI systems also permit visual inspection in areas that are hazardous to humans, such as toxic or very hot atmospheres. RVI systems generally have detachable tips. An inspector selects an appropriate tip for each inspection. Some tips permit not just capturing images of objects being inspected, but also capturing three-dimensional data of the shape of those objects. For example, phase-measurement tips project structured light patterns, e.g., parallel lines, onto inspection targets. Images of the targets are then captured. The phases of the structured light patterns as reflected off the targets depend on the distances between the pattern projectors and the targets. In various examples, differences between the absolute phases of the two separately-projected fringe sets are used to determine object distance.
However, the repeated attaching and detaching of tips, in addition to the environmental conditions in which they operate, can degrade or shift the performance of tips over time. For example, some tips include light sources. Those light sources can become caked with dust or other contaminants, reducing the light output. For tips using generally uniform illumination, such as phase-measurement tips, differential brightness reduction can reduce the accuracy with which 3-D data are measured.
Prior systems use a test block to perform verification of magnification on image-capturing tips. For tips used for 3-D measurements, test blocks can also be used to verify triangulation geometry. The test block includes a visible feature with a known size, and fixture to hold the tip in place with respect to the feature. To check magnification, a user inserts the tip into the test block and captures an image of the feature. The user then uses the normal measurement functions of the RVI system to measure the size of the feature. This generally includes manually positioning crosshairs, pointers, or other locators over portions of the feature, entering data about the tip and the test block into the RVI system, receiving a measurement between the crosshairs from the RVI system, and comparing that measurement to a known value. Although this type of verification can be useful, it is limited to simple dimensional measurement and is not suitable for more advanced tips such as phase measurement tips that can be used to take 3-D measurements.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.